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cases may bene fi t from botulinum toxin injections, which may lead to resolution of symptoms after a single treatment.

head, and abdomen and laughing or humming before speak ing, that temporarily reduce symptoms. 4 One of the important clinical characteristics of LD is its task speci fi city, that is, LD symptoms are de fi ned by selective impairment of speaking in ADLD, ABLD, and mixed LD, singing in SLD, and inspiration in ARLD. Patients with ADLD exhibit worse symptoms on voiced phonemes during counting from 80 to 90, whereas patients with ABLD have more di ffi culties with voiceless phonemes during counting from 60 to 70. In addition, shouting may di ff erentiate between LD subtypes as it is more challenging for those with ADLD due to increased e ff ort for voice projection. Conversely, whispered speech, overt emo tional speech, innate vocalizations (e.g., crying, laughing, and yawning), and other upper respiratory behaviors (e.g., coughing and sni ffi ng) remain intact 4,5 ( fi gure 1C). Based on LD task speci fi city, a series of vocal tasks, including sustained and repetitive phonations of vowels, pitch glides, shouting, counting, and overt and whispered production of sentences loaded with voiced or voiceless phonemes, are recommended for de fi ning LD and di ff erentiating it from voice tremor and muscle tension dysphonia. 4,5,7 Both voice tremor and muscle tension dysphonia a ff ect up to one-third of patients with LD and are often misdiagnosed as LD or vice versa. The central vs peripheral origin of hyperfunctional voice in muscle tension dysphonia remains unclear, 8 whereas understanding of the voice tremor spectrum is still being developed. 9,10 A recent consensus on tremor classi fi cation listed voice tremor as an additional clinical phenotype be yond the core criteria used to classify essential and dystonic tremor. 9 This is despite the fact that speci fi c clinical char acteristics that di ff erentiate between those with dystonic and essential voice tremor were published earlier by the Neu rolaryngology Committee of the American Academy of Otolaryngology — Head and Neck Surgery. 10 We view voice tremor as an umbrella diagnosis where dystonic voice tremor is characterized by task-speci fi c laryngeal tremor that co occurs with LD, whereas essential voice tremor a ff ects la ryngeal muscles either in isolation or in combination with other upper airway structures and/or extremities, is not task speci fi c, and may be present independent of LD ( fi gure 1C). In the majority of cases, voice and speech therapy and botulinum toxin injections into the laryngeal muscles are tried to help with di ff erential diagnostics ( fi gure 1B). LD symptoms typically do not respond well to voice and speech therapy, although indi viduals can bene fi t from treatment focusing on education, counseling, and e ff ective speaking strategies to address their heightened anxiety regarding social and occupational commu nication situations. Botulinum toxin injections are more e ff ective in ADLD than any other form of LD or voice tremor. Voice tremor symptoms may exhibit reduced symptom severity with behavioral therapy if able to modify their speaking patterns to shorten voicing duration. Conversely, symptoms of muscle tension dysphonia characterized by signi fi cant vocal e ff ort due to excessive tension in laryngeal and extralaryngeal muscles are typically relieved with behavioral therapy, although more severe

Other methods probed for diagnosis and di ff erentiation of LD from other voice disorders include high-speed videoendoscopy and laryngeal EMG. High-speed videoendoscopy showed promise for detection of distinct patterns of spasms a ff ecting vocal fold vibratory motion in LD vs muscle tension dysphonia and voice tremor. 11,12 However, its sensitivity and speci fi city need to be established before the wider application in clinical settings. Similar to other forms of dystonia, EMG is not used for LD diagnosis. 4 It o ff ers a qualitative rather than de fi nitive di agnostic value due to the fact that potentials are typically normal. However, laryngeal EMG combined with an acoustic channel may show a marked delay from the onset of an elec trical signal to the onset of acoustic output and as such might be useful in aiding the di ff erential diagnosis between LD, voice tremor, and muscle tension dysphonia. Summary, Gaps, and Priorities for Multidisciplinary Clinical Assessment and Diagnosis of LD c LD is a phenotypically complex and heterogeneous disorder that requires a multidisciplinary clinical ap proach for accurate diagnosis. c The current diagnosis of LD is based on a syndromic approach that is open to bias; thus, a diagnostic consensus between clinicians is hard to achieve. c Clinical diagnosis is a ff ected by the variability of LD symptoms, co-occurring conditions that mimic LD symptoms, and the experience and expertise of the clinician. c The access to health care professionals with the necessary knowledge and skills is a signi fi cant barrier. Less than 6% of speech-language pathologists work in a health care setting where patients with LD are likely to be seen. Only 2% of otolaryngologists are trained and specialized in laryngology. The proportion of movement disorder neurologists specialized in LD is likely far smaller. Specialized training of clinicians in LD and related disorders is critical for reducing misdiagnosis and delayed diagnosis. c Ultimately, the highest priority is clinical implementation of LD-speci fi c, pathophysiologically relevant biomarkers that are accurate, fast, objective, and cost-e ff ective in diagnosing LD and di ff erentiating it from other similar conditions. c Acceleration of a biomarker-based LD diagnosis neces sitates the identi fi cation of etiology and pathophysiology of this disorder.

Etiology of Laryngeal Dystonia Genes and Genetic Risk Factors

LD is characteristically multifactorial in its etiology, and ge netic variants are considered a signi fi cant risk factor for dis order development. It has been reported that up to 25.3% of

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Neurology | Volume 96, Number 21 | May 25, 2021 Neurology.org/N Copyright © 2021 American Academy of Neurology. Unauthorized reproduction of this article is prohibited.